The present invention relates, in general, to control equipment for the transmission of a motor vehicle and, more particularly, the invention is directed to a control mechanism for either an automatic or manual transmission that provides a balance between good fuel economy and engine performance of a motor vehicle equipped with the transmission control mechanism of the invention.
In vehicles equipped for manually shifting such vehicle's transmission, especially in commercial and utility type over-the-road vehicles, it may be the case that the torque for the newly selected gear to be shifted into is insufficient to permit driving the vehicle at the same speed which prevailed before the gear was shifted. When such a speed reduction occurs, it often times will require a down-shifting of gears in the transmission. The judgment and anticipation by the driver of the vehicle of such an adverse occurrence is difficult at best, and may not always be accurate for a number of reasons. An incorrect estimation or prediction by the driver, which brings about a faulty shifting, almost always results in an uneconomical vehicle operation. This is especially true in regard to a higher fuel consumption. Furthermore, such predictions by the driver, based on his judgment alone, are very difficult and therefore they are often imprecise.
The situations described above can also be incurred with vehicles equipped with transmissions for automatically shifting gears. Such automatic transmission gears are therefore designed in such a way that they can only be shifted into a new gear position if and when a high torque, or performance reserve, is available. In some cases, an extremely high torque reserve is required before shifting such gears can occur. This means that the operation of the vehicle thus equipped is also uneconomical, especially with regard to lower fuel consumption.
The selection, or choice, of the most advantageous point of operation for a vehicle drive train, consisting of a motor and a gear transmission, depends on many factors. A number of these factors are outside the control of the driver. Even a definition of the term "best or most advantageous operating point" is difficult, because the point of the most economical fuel consumption, as represented by a family of curves relating to the motor characteristics, is not necessarily the point of maximum motor performance and/or output. Depending on operating requirements and other outside conditions, the selection of the gear speed must be varied for economical operation between criteria selected from several different operating points, which was considered operationally "advantageous". The quality and value of such selected criteria will heavily depend also on the ability to maintain constant the level of the value or data selected. This is not easily accomplished. If, for example, motor torque is determined as one of the motor factors selected as a criteria; then such determination is dependent on the fuel density, the elevation at which the motor is being operated, the fuel quality, the motor temperature, and others. If the motor factors, such as the data representing the motor torque, are compared with either theoretically or empirically derived constants, the result will often show a flaw as soon as even one of the many influence factors enumerated and discussed above shows a deviation.
An immediate task that could represent one possible solution for eliminating such flaws and to overcome the above problems, would be to gather as much data as possible on as many of the influence factors as possible, and to evaluate the collected data on them on their own terms. To accomplish this would require the use of an appropriate individual sensor for each individual factor. This would, however, constitute a great expense that probably cannot be justified.
In addition, the precision and accuracy with which a given value can be determined is of great importance with respect to determining the shifting points for the transmission gears, especially in connection with commercial and utility vehicles, which have a large ratio between load and empty operations. If, for example, the drive resistance occurring on the vehicle at a more or less substantially constant velocity is to be accurately determined for such vehicle; then the values and data for this selected criteria, such as any changes in the air resistance coefficient C.sub.W, would have to be examined regarding various structural or design modifications, air density, changing rolling friction of the tires against the roadway at various tire profiles, pressures and wear conditions and friction conditions (i.e., wet or dry roadway surfaces), roadway cross-section, etc. would also have to be determined. Added to this fact, it should also be pointed out that specific values for certain data, such as bearing friction and gear efficiency, cannot be determined at a reasonable cost for standard vehicles which are mass-produced. This serves to further compound the above-discussed problems of gear selection relating to the achievement of good economy with respect to fuel consumption while retaining good performance on the vehicle engine.